This invention relates to an ignition system for a marine propulsion unit and more particularly to an improved ignition system that will prevent hunting of engine speed in response to changes in engine load.
It is well known to provide modern spark ignited internal combustion engines with electronic spark control circuits. Such electronic spark controls are operative to control the ignition timing in response to changes in throttle position and changes in engine speed. Such devices are highly effective in most applications.
However, in many applications for an internal combustion engine the load on the engine can change without any operator control input and such changing loads can, unless otherwise compensated for, change the speed of the vehicle being propelled by the engine and also, of course, the engine speed. For example, most electronic ignition controls are effective so as to retard spark timing when the engine speed is slowed and to advance spark timing when the engine speed increases. As a result, if traveling at a given speed and the load on the engine increases, the speed will decrease. This will inherently cause a reduction in the spark advance which causes a further speed reduction. On the other hand, if the speed of the vehicle increases due to a reduced load, then the spark advance will increase and the engine and vehicle speed will continue to increase. These problems are particularly acute in connection with applications in water vehicles wherein the wave pattern can cause frequent changes in load on the engine.
It is, therefore, a principal object of this invention to provide an improved spark control arrangement for an internal combustion engine wherein the engine speed will be maintained constant with changes in load.
It is a further object of this invention to provide an automatic spark advance system for an internal combustion engine which is responsive to engine speed and throttle position and which will maintain a constant speed of the engine in response to varying loads and when the throttle position is held constant.
It is a further object of this invention to provide an improved ignition system and electronic ignition control for a marine application.